A capital replacement program would have replaced a large amount of pipe in good condition

DPW's Challenge

To meet its 2005 Consent Decree, DPW needed to assess the condition of its non-redundant force mains. In order to effectively assess force mains that could not be shut down, DPW required advanced non-destructive methods that could provide condition data while the lines remained in service.

Pure’s Assess & Address approach to pipe¬line management is built on extensive research and data from over 8,000 miles of pressure pipe inspec¬tion which has found that less than 1 percent of pipelines need immediate repair. Assess & Address programs focus on identifying vulnerable areas of a pipeline and completing selective rehabilitation and replacement in favor of full-scale capital replace¬ment, often saving the utility millions of dollars.

What was the Solution?

Although the Consent Decree stipulated that the force mains be inspected, it allowed DPW the flexibility to specify the method or technology at the time the inspections were performed. DPW took this opportunity to go beyond a minimalist approach, choosing to inspect its force main inventory with advanced non-destructive condition assessment technologies.

DPW contracted two engineering firms to inspect its wastewater force mains.Both firms subsequently contracted Pure Technologies for leak and gas pocket detection along with condition assessment of the force mains.

As part of the overall condition assessment of PCCP force mains, leak and gas pocket detection is important since their presence is often a preliminary indicator of a potential failure location.

Gas pockets in force mains are of significant concern as hydrogen sulfide gas within the wastewater may be converted to sulfuric acid by bacteria in the slime layer on the pipe wall, which may cause corrosion and eventual breakdown of the pipe’s exposed surface.

DPW used SmartBall Technology for leak and gas pocket detection; the tool is free-swimming and measures the acoustic activity associated with leaks and gas pockets in pressurized pipelines.

For structural condition assessment of the force mains, DPW used the PipeDiver® and PureRobotics® EM condition assessment platforms. The PipeDiver tool is a free-swimming EM platform that is able to locate and quantify the amount of wire break damage in PCCP. It is the best method of determining a baseline condition of a PCCP pipeline that cannot be removed from service.

The PureRobotics tool is an EM inspection platform that also contains a CCTV camera and SONAR; the tool takes a magnetic signature reading and quantifies the amount of wire breaks using the same method as PipeDiver technology

Procedure

In July 2011, Pure Technologies completed the initial phase of the project with DPW, completing an EM condition assessment and a leak and gas pocket survey on the 54-inch Patapsco Force Main in Baltimore County. The inspection covered the entire 1.5-mile alignment.

The Patapsco inspection was Pure’s first sewer force main EM inspection using PipeDiver, and the first in-service assessment of a PCCP force main in the world.

In the subsequent 2012 force main program, DPW and Pure Technologies completed just over 15 miles of SmartBall leak detection, almost 11 miles of PipeDiver condition assessment, and about 3 miles of robotics inspection on 11 different force mains. The pipe diameters varied for each force main, ranging from 16-inch to 42-inch PCCP.

Results

Of the 423 pipes inspected in the Patapsco Force Main, 24 pipes showed clear indications of distress for just fewer than 6 percent of the total pipeline. The results from the Patapsco SmartBall survey showed no anomalies associated with leaks or gas pockets.

Based on the PipeDiver inspection and subsequent Finite Element Analysis (FEA) of the Patapsco Force Main, a number of pipe sections exhibited prestressing wire breaks that suggested the pipeline had several sections with deteriorating conditions. It was recommended that the Baltimore County DPW start a high priority program for repair or replacement of several pipe sections based on the results of the FEA to reduce the risk of pipe failure. It was also suggested that the Patapsco Force Main should be re-inspected within five years to reassess the risk of failure and develop a deterioration model for the pipeline.

Of the 2,810 pipes that were inspected in October and November 2012, 99 showed signs of distress for about 3.5 percent of the total pipeline. The results from the SmartBall leak detection survey identified no leaks and 7 pockets of trapped gas.

To date, Pure has recommended that less than 0.5 percent of the identified deteriorated pipes be repaired, allowing DPW to safely manage its force mains and avoid unnecessary repairs.

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